Android: Smartphones have been controlling computers with specialised apps for years now, but Mac Remote does something a little different -- it doesn't require you to install any server software to work. Instead, it connects to your Mac over SSH and controls various apps and system functions with remote commands.
Although you don't have to install anything, you do have to enable Remote Login on your Mac (which you do in the Sharing panel of System Preferences). If you don't know how to do this, Mac Remote will teach you how when you run it for the first time.
Once you're set up, you'll be able to control the brightness and volume of your Mac, as well as applications such as Preview, iTunes, VLC, iPhoto and Spotify.
Although imperfect and ad-supported, Mac Remote works well. If you need a simple method of controlling your Mac via your Android phone or tablet, this free download can help.